This invention relates to a room temperature wet chemical growth (RTWCG) process of SiO-based dielectric coatings on semiconductor substrates and layers including but not restricted to Si, Ge, III-V and I-III-VI, and II-VI compound semiconductors and, specifically, to the RTWCG of SiO-based films on Si in the manufacture of silicon-based electronic and photonic (optoelectronic) device applications. One particular application involves the use of this room temperature wet chemical growth process to make SiO based thin film oxide layers with low metallic and non-metallic impurity concentration for use in the next generations IC microelectronic devices.
Silicon dioxide (SiO2) forms the basis of the planar technology. In industrial practice dielectric coatings for electronic and photonic devices layers are most frequently formed by thermal oxidation of Silicon (Si) in the temperature range 900 to 1200xc2x0 C. SiO2 is also deposited by chemical vapor deposition (CVD) techniques at lower temperatures (200 to 900xc2x0 C.) on various substrates.
Thermal and CVD-grown SiO2 based layers are used as diffusion masks, to passivate device junctions, as electric insulation, as dielectric material in Si technology, and as capping layers for implantation-activation annealing in III-V compound semiconductor technology, to name a few.
The growth of dielectric films at low temperatures is very attractive for most device applications due to reduced capital cost, and high output and technological constraints associated with the growth of dielectric thin films using conventional high-temperature growth/deposition techniques.
Dielectric films for microelectronic/photonic (optoelectronic) devices are well known in the art and are usually deposited at near room temperature on various substrates using physical vapor deposition processes including conventional (nonreactive) or reactive resistive, induction or electron beam evaporation, reactive or nonreactive dc or RF magnetron and ion-beam sputtering processes.
Room temperature growth of dielectric layers on semiconductor surfaces using anodic oxidation is known in the art. For silicon, using anodic oxidation up to 200 nm SiO2 layers can be grown on the underlying Si substrates. The anodic oxidation process consumes about 0.43 of the thickness of the oxide from the underlying Si substrate, and is not compatible with most metallization schemes. This limits its application as a replacement of thermal or vacuum deposited SiO2.
Deposition of SiO2 dielectric layers from solutions is known in the art using organo-metallic solutions. In this procedure, the dielectric layer is applied onto the substrate either by dipping the substrate into the solution or by spinning the substrate after a small amount of the solution is applied onto the surface. In both cases the substrate is then placed in an oven to drive off the solvent.
Researchers from Japan, China and Taiwan describe processes for deposition of SiO2 and SiO2xe2x88x92xFx layers on glass and silicon surfaces using a room temperature (30 to 50xc2x0 C.) solution growth. The growth of liquid-phase deposited (LPD) SiO2, initially proposed by Thomsen et al. for deposition of SiO2 on the surface of soda lime silicate glass, is based on the chemical reaction of H2SiF6 with water to form hydrofluoric acid and solid SiO2. The initial H2SiF6 solution is saturated with SiO2 powder (usually in a sol-gel from). Before immersing the glass into the solution, a reagent that reacts with the hydrofluorosilicilic acid, such as boric acid, was added to the solution. Boric acid reacts with the hydrofluorosilicilic acid and makes the solution supersaturated with silica.
One of the major disadvantages of SiO2 LPD method described above is a very low deposition rate of about 8 nm/hour to about 24 nm/hour, which makes it impractical for growing dielectric layers for most semiconductor device applications. Deposition rates of up to 110 nm/hour are claimed by Ching-Fa Yeh et al. in the hydrofluorosilicilic acid-water system and the composition of the resulting films was reported to be SiO2xe2x88x92xFx where x is about 2%. Our own experimentation using the LPD method, seems to indicate that the LPD SiO2 has poor adhesion to the Si surfaces, and the maximum growth rate we obtained is smaller than the reported values (less than 25 nm/hour). Even assuming that the reported 110 nm/hour deposition rates are possible, these deposition rates are still too low since assuming that the deposition rate is constant with the deposition time, it will require about 9 hours to deposit an oxide with a thickness of about 1 xcexcm needed for ULSI interlevel dielectric.
The U.S. Pat. No. 6,080,683, entitled xe2x80x9cRoom Temperature Wet Chemical Growth Process of SiO Based Oxides on Siliconxe2x80x9d issued Jun. 27, 2000 and the U.S. applications Ser. No. 09/602,489 entitled xe2x80x9cRoom Temperature Wet Chemical Growth Process of SiO Based Oxides on Siliconxe2x80x9d and U.S. applications Ser. No. 09/891,832 entitled xe2x80x9cMethod of Making Thin Films Dielectrics Using a Process for Room Temperature Wet Chemical Growth of SiO Based Oxides on a Substratexe2x80x9d which were filed on Jun. 23, 2000 and Jun. 26, 2001, respectively as a continuation-in-part of the above patent, describe a room temperature wet chemical growth (RTWCG) process and method for growth of a silicon oxide layer on a semiconductor substrate to produce a silicon oxide layer comprising:
a) providing a substrate;
b) providing a reaction mixture comprising a silicon source, a pyridine compound, and an aqueous reduction oxidation solution;
c) a catalyst to enhance the reaction, and
d) reacting the mixture with the substrate to form said silicon oxide layer;
High growth rates of SiOX oxides according to related art described above are grown on planar or porous silicon using, commercial grade organic and inorganic silicon sources, a pyridine compound, such as N-n butylpyridinium chloride (C9H14CIN), redox aqueous solutions based on Fe2+/Fe3, an organic or inorganic homogeneous catalyst, and non-invasive additives to adjust the pH of the growth solution. By using the above growth solutions formulations, the SiO based oxide layers grown on various semiconductor substrates have a lower growth rate and a higher metallic and non-metallic impurity concentration, and inferior electric and dielectric properties compared with the SiO-based oxide layers grown using the solution growth formulations described in this patent application.
The term RTWCG process of SiO-based dielectric layers as used herein means a room temperature (e.g. 10-40xc2x0 C.) wet chemical growth process for silicon oxide layers. While this layer is referred to in this application as a xe2x80x9csilicon oxide layerxe2x80x9d, this means a layer which is SixOyXz (SiOX) layers where x is from 0.9 to 1.1, y is from 0.9 to 1.1 and z is from 0.01 to 0.2, where Si stands for silicon, O stands for oxygen, and X is either fluorine, (F), carbon (C), nitrogen (N) or a combination of these with iron (Fe), palladium (Ti) or other trace amount of metallic and non-metallic contaminants, depending on the redox system, catalyst, and the non-invasive additives being used.
One useful definition of a xe2x80x9ccatalystxe2x80x9d is a compound that promotes the reaction wherein the metallic ion of the reduction oxidation solution is subject to a change in its electron state such as from Fe2+ to Fe3+. Also, a homogeneous catalyst is a catalyst which is dissolved in the reaction solution.
This invention relates to a room temperature wet chemical growth (RTWCG) process of silicon oxide (SiO) based thin film dielectrics with low metallic and non-metallic impurity concentration on semiconductor substrates and, specifically, to the RTWCG of SiO-based films in the manufacture of silicon-based electronic and photonic (optoelectronic) device applications.
It is an object of the invention to provide a silicon oxide-based thin film dielectrics with low metallic and non-metallic impurity concentration on a semiconductor substrates using a room temperature wet chemical growth (RTWCG) process for electronic and photonic (optoelectronic) device applications that uses solutions growth solutions comprising of organic and inorganic components, that are compatible with device fabrication steps, have large growth rates, low stress, good adhesion to silicon surfaces, is stable on long term air exposure, and high temperature annealing, and that has good conformity.
It is a further object to provide a silicon oxide-based RTWCG process of low dielectric constant SiO based films for use as intermetallic dielectric (IMD) in ultra large scale integrated (ULSI) silicon based microelectronics.
It is a further object to provide an ultra thin film silicon oxide-based RTWCG process to be used as gate dielectric for ULSI silicon based microelectronics.
It is a further object to provide a silicon oxide-based RTWCG process of thin film dielectrics to be used as passivation layers for photonic (optoelectronic) device applications.
It is a further object to provide a silicon oxide-based RTWCG process to grow passivating/antireflection coatings, after the front grid metallization for the fabrication of low cost silicon solar cells and for other photonic (optoelectronic) device applications.
It is a further object to provide a silicon oxide-based RTWCG process to be used as passivating films for porous silicon coated photonic (optoelectronic) devices.
High growth rates of SiOX oxides according to this invention are grown on planar or porous silicon using commercial grade inorganic or organic compounds including but not limited to H2SiF6 (34%) or other silicon containing salts such as ammonium hexafluorosilicate (NH4)2SiF6 as silicon source, with or without the electron exchange pyridine based component. The growth system according to this invention is also comprising of a solution containing metallic ions Me+n/Me+(n+m) where n=0 to 4, and m=1 to 4, a list of which includes but is not restricted to transitional metallic ions such as Ti, Co, V, Cr, Fe, Ni, Cu, Y, Sr, Ce, Ba, Zr, Nb, Ru, Rh, and Pd that enhances the growth and lowers the concentration of the metallic impurities within the SiO-based thin film. The role of the various classes of the above metallic ions are to provide a reduction oxidation (redox) aqueous component such as Fe2+/Fe3, e.g. K3Fe(CN)6, a catalyst such as H2TiF6 aqueous component that added to the growth solution is used to enhance the growth of the SiO based thin film, and non-invasive additives that include but are not restricted to NaF, KOH, NaF and NH4F and HF, HCl, H2SO4, and H2O2 that are used according to this invention to adjust the pH of the growth solution, and vary the growth rate, and/or reduce the concentration of metallic and non-metallic impurities within the RTWCG SiO based film.
In a preferred embodiment of the invention, we are substituting all organic components of the growth solution with inorganic components, by using only inorganic components for the silicon source, eliminate the pyridine based components, and use various inorganic combinations for use as redox and catalysts components added to the growth solution from among the non-invasive additives aqueous components based on Me+n/Me+(n+m) where n=0 to 4, and m=1 to 4. The new SiO based oxide layers grown on various semiconductor substrates have a higher growth rate and a lower metallic and non-metallic impurity concentration, and better dielectric properties compared with the SiO-based oxide layers grown using growth solutions that contain organic components.
The RTWCG rate on Si surfaces is from 1 nm/minute to over 100 nn/minute, depending on the composition of the growth solution. The chemical composition of the grown layer has the general formula: SixOyXz, where the significance of Si, O, X, and x, y and z are as explained above.